Patent GB-190424675-A (GB)
Title: Improvements in Electric Brakes for Trams and other Vehicles.
Inventor: RANSFORD ROBERT BOLTON
Filed: 1904-11-14
Granted: 1905-02-23
Abstract: 24,675. Ransford, R. B., [American Electric Co.]. Nov. 14. Brakes, electric. The current for operating the brake magnet on a tram or other vehicle is supplied at low speeds by the trolley wire, but at high speeds by the motors acting as generators, part of the current being passed through the operating-coil of an automatic r e g u - l a t i n g-switch so that the braking power diminishes with the retardation of the vehicle. The apparatus and circuits are shown diagrammatically in Fig. 1, and a modified arrangement for a multiple-unit system is shown in Fig. 23. The apparatus comprises, besides a power switch PS, a reversing-switch RS, and a brake switch BS, a brake magnet M, shown in Figs. 15 and 17, adjacent to it being a release coil RC, Figs. 1 and 17, which operates a mechanism for gripping and releasing the brake magnet. A transfer switch TS, Fig. 1, which transforms a series circuit through the brake-magnet coils B<2> ... B<5> into parallel circuits across the terminals of the armatures A', A' of the motors M', M<2>, is operated by the current in the coil TC after passing through the coil AC of the automatic controlling-apparatus A, or through the controlling-apparatus itself, or through the shunts S', S' and the resistances AR in connection with it. The brake switch BS may be moved into six positions, the running position being that in which the contacts on the vertical line 2 touch the brushes T<2>, b<1>, b<19>, a', &c. In this position, the current from the trolley arm T passes to the motor M<1> through the contact T' and the power switch PS, (which is in the position a, b), the power resistance PR, the brake switch BS, the reversing-switch RS (which is in the forward-running position f), to the armature A<1>, and back through the reversing- switch RS and the brake switch BS to the field coils F<1> of the armature A<1>; thence through the brake and power switches to the ground G. A similar circuit operates the motor M<2>. In the position 1 of the brake switch BS, the current passes to the transfer switch TS and through the coils B<2>, B<3>, B<4>, B<5> of the brake magnet M, which coils, in this position of the transfer switch, are in series, and through the release coil RC to the ground G, so that the trolley current, passing through the release coil, frees the brake magnet, as described below. In the first braking position of the switch BS, as indicated by the line 3, the motors act as dynamos and supply current to the brake magnet. The circuit from the motor M<1> is through the reversing and brake switches to the automatic controlling-apparatus A, thence to the transfer coil TC and the coil B' of the magnet M, and back through the resistance AR and the spring-controlled bridge ab of the controller A to the brake switch, and then to the field coil F<2> of motor M', the brake and reversing switches, and to the armature A<1>. The circuit from the motor M' is similar, and includes the field coil F<1> of the motor M', so that the field of one motor is excited by the current generated by the other. The trolley current is also led to the brake magnet, passing through the coils B<2> ... B<5> in series. In this position, the release coil RC is placed in shunt to the armature A' so as to unlock the brake magnet. A rise in the motor current in the transfer coil cuts off the trolley current in the brake-magnet coils and places the coils B', B<3> of the brake magnet M in parallel across the terminals of the armature A', and the coils B<4>, B<5> across those of the armature A'. The current passing through the coil B<2> ... B<5> has already passed through the actuating-coil AC of the controller A, and is therefore regulated by the resistance AR. In the position 4 of the brake switch, the shunt S' is placed in the circuit so as to lessen the current in the coil AC of the controller A, so that the bridge ab moves back and cuts out the resistance AR, and thus increases the current in the coils B<2> ... B<5> of the brake magnet M. In the position 5, a smaller resistance S' is thrown into the circuit, and in the position 6 both shunts S<1>, S<2> are thrown in. If the reversing-switch RS be placed in the position r, the circuit from the armature A' is through the reversing and brake switches to the field coils F' of the motor M', and then through the brake switch BS to the field coils F<1>, back to the brake switch, to the armature A', and then through the reversing brake, and reversing switches in succession to the armature A<1>, so that the system is equivalent to two series-wound generators in multiple without equalizing-connections. In a modified arrangement, shown in Fig. 10, the shunts S<1>, S' and the transfer switch are omitted, and the variation in the current in the brake-magnet coils is produced by cutting out parts of the operating-coil AC of the automatic controller A. The circuits are arranged so that the voltage generated by the motors opposes the trolley-current in the brake-magnet coils B<6>. An additional coil AL is fitted to the controller A, and is placed in the trolley-current circuit so as to facilitate the regulation of the current delivered by the motors to the coils B<7>, B<8>, B<9> of the brake magnet M. The brake magnet consists of a cylindrical iron body D, Fig. 15, within which are placed the coils B<2> ... B<5> surrounding the plunger M. The rear end J is provided with an inwardly-projecting pole-piece K, which is made of metal with magnetic qualities superior to those of the head J. A non- magnetic tube Z protects the coils and guides the plunger M, which is tapered as shown so as to extend beyond the pole-piece K. The area of the air gap therefore decreases relatively to its decreasing length as the plunger moves inwards, and maintains a constant pull on the plunger. When the braking- current ceases, the plunger M, moving forwards, jams the roller h under the inclined block n, and locks itself until the block n is allowed to rise by the upward movement of the cam d on the spindle V, Fig. 17. The cam is normally kept down by the adjustable spring pin q, and is raised by the current in the release coil RC drawing in the core o and rocking the spindle V. Similar solenoids may be used for the transfer switch TS and for the automatic controlling-apparatus A, the return movements being effected by springs. Fig. 21 shows a modified form of the automatic controlling - apparatus. The current passes through the coils AC, AL in the casing 52, and the plunger 42, sliding in the non-magnetic tube 43, is attracted towards the pole 51 in the hood 50, and compresses the adjustable spring AS' by means of the non-magnetic rod 44 bearing upon the head 45. The insulated cross-bar ab attached to a rod of the plunger 42 is thus moved over its contacts ac, which are connected to the clamps 59 on the resistance AR adjacent to the apparatus. In the multiple-unit system shown in Fig. 23, the brake switch BS is movable to only two positions 1, 2 ; it is held in position 2 by the spring CS, and in position 1 by the solenoid cm, the circuit through which is completed when the master-controllers mc are in the running position 2<a>. In the release position 1<a>, the circuit of the train-cable conductor R is completed through the line and release coil RC to the ground. In the position o, all the circuits are open. In the position 3<a>, the circuit is from the conductor T<8> to the conductors 61, 62, 63, and thence through the operating-coils of the magnets LM, SM<1>, SM<2>, the magnet LM closing, at 64, 65, the circuit from the trolley wire, brake switch, and wire T<4>, and through the resistance lr and the coil B<6> of the brake magnet m. In the position 4<a> of the master-controller, the circuit of the magnet SM<2> is closed and that of the magnet SM<1> is open and the shunt S' is thus introduced into the braking-circuit. In the position 5<a>, the circuit of the magnet SM<1> is closed, and that of the magnet SM<2> is open, and the shunt S' is placed in the circuit. In the position 6<a>, the circuits of both magnets SM<1>, SM<2> are open and both shunts are placed in the brake circuit. The brake magnet m is wound so that all the current passing through the coils B<7>, B<9> and the field windings of the motors also passes through the coil B<8>. The construction shown in Fig. 23 applies the brakes with maximum effect when there is no current in the train cable, should, for instance, the train break in two parts.